1. Field of the Invention
The present invention relates to a configuration of an image scanning apparatus suitably used to place and scan a large amount of documents.
2. Description of the Related Art
For example, Japanese patent Publication Laid-Open No. 2006-16093 discloses a copying machine which includes an upper-limit position detection sensor for detecting a topmost document while being able to place plural documents on a document tray (document feeder tray). In the copying machine disclosed in Japanese patent Publication Laid-Open No. 2006-16093, when the number of documents is decreased as the documents on the document tray are fed, a control device controls a tray driving mechanism to always keep the topmost document at the same position with respect to a pickup roller according to a detection result of the upper-limit position detection sensor. Therefore, the topmost document is always located at a position where the document can be fed.
In the large-capacity image scanning apparatus as disclosed in Japanese patent Publication Laid-Open No. 2006-16093, with the increasing need for short time copying of a large amount of documents, there is a strong demand to perform high speed scanning while maintaining the scanning image quality.
However, in Japanese patent Publication Laid-Open No. 2006-16093, there is no description concerning the timing for controlling the tray driving mechanism to lift and lower the document tray. Accordingly, in Japanese patent Publication Laid-Open No. 2006-16093, when the document tray is elevated during scanning of the document, the document is possibly moved by an elevation of the document tray during transportation of the document, resulting in deterioration of the scanning image quality.